3.15 Iatrogenic spinal deformity

Iatrogenic spinal deformity is an abnormal alignment of the spine which is caused by medical treatment.

There are three main causes of iatrogenic deformity:

Teratogenic events can lead to spinal maldevelopment in utero.

This is a relatively common complication of spinal surgery in adults. It is caused by excessive removal of the posterior elements of the spine and/or a failure to recognize lesser spinal deformity in the coronal or sagittal plane prior to surgery because sole reliance has been placed upon magnetic resonance imaging for preoperative assessment. Spondylolisthesis due to excessive facet (zygopophyseal) joint resection is the most common problem but lateral subluxation (especially at L4/5 and less so at L3/4). The integrity and orientation of the facet joints is critical to spinal stability. If more than 50% of the facet joint is excised, there is a significant risk of subluxation. This may precipitate spinal stenosis (see Chapter 3.8). The recognition of this complication by spinal surgeons has reduced the incidence of this complication. The identification of an underlying spinal deformity must be identified preoperatively so that the problem is not exacerbated by injudicious decompression.

Multilevel laminectomies in children (usually for the treatment of spinal tumours) have a high incidence of late kyphosis. This occurs in up to 50% of children undergoing multilevel cervical laminectomy. The younger the child at the time of surgery, the more likely it is that deformity will occur. The facet joints are more horizontal in children than adults and therefore the risk of kyphosis is greater. In the young, the initial kyphosis may lead to anterior wedging of the vertebrae, resulting in further kyphosis. The posterior ligaments and the paraspinal musculature also play an important role in maintaining the sagittal profile of the spine. Disruption of these during major surgery may encourage kyphosis. Kyphosis is the most common deformity following multilevel laminectomy and is progressive with a risk of neurological deficit. The level of the surgery is important. The cervical spine is most at risk, followed by the thoracic spine (Figures 3.15.1 and 3.15.2). The lumbar spine is rarely affected.

Scoliosis rarely occurs following laminectomy and is usually caused by the pathology which precipitated the original surgery or its treatment. Scoliosis may be a presenting feature of a spinal tumour (Figure 3.15.3). Surgical excision of the tumour does not prevent progression of the curve.

Lordosis of the spine, producing a characteristic swan-neck deformity, may be seen following multilevel cervical laminectomy. Lordosis also occurs as a compensatory effect above an iatrogenic thoracic kyphosis and in the lumbar spine after extensive laminectomy.

Prevention is the most effective method of treating this condition. Surgeons should try to preserve the posterior structures, especially the facet joints and ligaments. Liaison between the neurosurgeon and the orthopaedic spinal surgeon are important with prevention and appropriate primary surgery being preferable to revision surgery and stabilization. Laminoplasty (instead of laminectomy) has been shown to have a reduced incidence of kyphosis in the cervical spine in children. Instrumented spinal fusion at the time of surgery may be appropriate; for example, in spinal stenosis with coexistent degenerative spondylolisthesis.

Long-term postoperative follow-up is mandatory, especially in the young patient at risk. External support by bracing or a halo-jacket may be helpful in preventing progression. If the deformity is progressive, in situ fusion or correction and fusion are the best approaches. A combined anterior and posterior approach will be necessary for correction of a kyphosis.

Ligament reconstruction has been described for postcervical laminectomy deformity. The theoretical advantage of this technique over fusion means that the growing child can gain some longitudinal growth and not be doomed to a shortened cervical spine. This may occur if the neck is fused at a young age, preventing further growth.

The removal of ribs in a growing child can destabilize the thoracic spine and lead to the development of scoliosis. The more ribs that are removed, and the closer the ribs are resected to the spine, the worse the resulting deformity. The curve deviates with the convex side to the side of the rib resection. In the developed world, the most common cause of thoracogenic deformity is the resection of multiple ribs for the treatment of malignancy. Elsewhere, tuberculosis is the main cause of this deformity.

Conservative treatment is not usually possible. The absence of lateral ribs prevents the application of a brace to apply pressure to the spine. Instrumented correction and stabilization are required for progressive curves.

Radiotherapy is used as a treatment for childhood tumours, such as Wilms’ tumour and neuroblastomas. The normal growth of the spine may be affected, leading to spinal deformity. The epiphysis is particularly susceptible to radiation damage. The first case of scoliosis induced by radiation was described by Arkin and colleagues in 1950. Skeletally immature patients who receive more than 1000cGy are at risk. The risk of deformity increases with the amount of radiation absorbed. Asymmetric radiation is more likely to lead to scoliosis and symmetric radiation may lead to a kyphotic deformity. In another study, it was noted that 59 out of 81 patients who had radiotherapy for Wilms’ tumour developed a subsequent scoliosis.

The younger the patient at the time of exposure to radiation, the more risk there is of spinal deformity. Patients aged less than 2 years at the time of radiotherapy are particularly at risk.

All paediatric patients undergoing spinal irradiation require follow-up by an orthopaedic surgeon or spine specialist until skeletal maturity. The principles for bracing or surgical management are the same as those for idiopathic deformity (Chapter 3.10). The risk of pseudarthrosis and infection is high, and healing may be prolonged if surgery is undertaken.

The importance of iatrogenic deformity lies in its recognition and prevention. This is certainly true for postlaminectomy deformity. Reducing the extent of surgery on the thoracic cage will decrease the risk of post-thoracotomy deformity. Radiation therapy is likely to generate spinal deformity, and these patients require vigilant follow-up. In adults, the most common deformity occurs as a result of a failure to fully appreciate the position of the spine preoperatively followed by injudicious decompressive surgery.